1. Field of the Invention
The present invention relates broadly to prostheses. More particularly, this invention relates to ophthalmologic prostheses, and even more particularly to punctum plugs.
2. State of the Art
The surface of the eye and the inner surface of the eyelid are lubricated by tear fluid constantly produced by glands around the eye. A tiny hole, known as the lacrimal punctum, located at the medial margin of each of the upper and lower lid margins drains the tear fluid away into the nasal lacrimal ducts.
A variety of eye problems are related to an insufficient volume of lubrication at the surface of the eyes. The most common is keratoconjunctivitis sicca, also known as dry eye syndrome. A common cause for the insufficient tear volume is the drainage of too great a volume of tear fluid through the punctal opening, the lacrimal duct, and into the nasal passage, thereby removing the tear fluid from where it is needed at the eye surface. Contact lens wearers particularly suffer when there is insufficient tear fluid volume at the ocular surface. In addition, dry eye is a component of various ocular diseases such as corneal ulcers, conjunctivitis, pterygium, blepharitis, keratitis, red lid margins, recurrent corneal erosion, filamentary keratitis and other external eye conditions.
A number of methods for closing the punctal opening have been used to retain tear fluid at the eye surface to prevent or alleviate dry eye syndrome, including suturing, laser sealing, and plugging. Plugging with a punctum plug is the least severe solution, is relatively inexpensive, and is being performed with increasing frequency.
In addition, punctum plugs may be useful in decreasing contact lens intolerance, for increasing retention/enhancement of ocular medications on the eye, for maintenance of ocular flora, for punctal stenosis, and to enhance healing and comfort after surgery.
A punctum plug typically includes an elongate shaft having a proximal end and a distal end, a head at the proximal end of the shaft, and a relatively larger body at the distal end of the shaft for occluding the lacrimal punctum. The plug is usually provided with a proximal axial bore for receiving a removable insertion tool.
In the current punctum plug insertion procedure, the sphincter muscle about the punctal opening is dilated with a dilator and an insertion tool, on which the plug is mounted, is used to maneuver the plug towards the dilated punctum. Force is then applied to the insertion tool to move the body of the plug through the punctal opening, the muscles of the punctal ring, and into the vertical punctum of the lacrimal canaliculus until the plug is fully inserted. The plug is fully inserted when the head seats against the tissue at the punctal opening and the body seats within the lacrimal punctum and vertical canaliculus so as to block the passage of tear fluid into the punctum and thereby retain tear fluid at the surface of the eye. Once the plug is fully inserted in the punctum, the insertion tool is decoupled from the plug and withdrawn.
Plugs are generally provided in several sizes to accommodate different sizes of lacrimal punctum so that the plug will achieve a good fit. That is, the plug should block drainage of tear fluid for a given patient's punctum size, the plug should fit stably within the punctum and not be subject to inadvertent release, and the plug should be relatively comfortable for the patient. For example, punctal dilation tends to permit plugs that are too large for a particular punctum to be inserted therein. Then, once the punctal opening reassumes its natural size, the plug may cause irritation to the recipient. In addition, the stress of a plug too large for the particular punctum may undesirably permanently stretch the punctal anatomy. In addition, it is not uncommon for plugs to be inserted into a punctum that are too small for that punctum, and such plug then being prematurely extruded, often within days of implantation. Therefore, it is necessary for the treatment provider to stock a range of size of plugs so that the correct size can be implanted in the patient.